Originally Posted by
safetypee
So if the thrust has not changed and the revised engine mount might not contribute a significant pitching moment, then why introduce MCAS.
This has been extensively discussed previously on this thread, and in several news articles. MCAS has nothing to do with thrust. MCAS has everything to do with lift. The nacelle on the 737 MAX is larger than the nacelle on the 737 NG. The center of pressure of the nacelle is also forward of the center of gravity, on both aircraft. At very high angles of attack, the nacelle begins to generate some amount of lift. Because the Cp(nacelle) is forward of Cg(aircraft), this causes a nose-up pitching moment. Because the nacelles are larger on the MAX than on the NG, and they are mounted further forward of the wing on the MAX, the nose-up moment is larger on the MAX than on the NG. The intent of MCAS is to feed in nose-down stab trim to counteract the nose-up moment caused by the lift from the larger nacelles.
Further explanation, with pretty graphics:
https://leehamnews.com/2018/11/14/bo...to-the-pilots/